Engine oil viscosity has a direct effect on engine friction, which in turn affects engine idle speed and engine torque output. Engine oil viscosity also affects oil pressure and systems which rely on oil pressure to operate, for example variable camshaft timing (VCT) systems. Engine control strategies, including engine idle speed control and electronic throttle control, therefore must compensate for changes in engine oil viscosity (and/or engine friction) in order to properly determine the amount of air and fuel required to achieve a given idle speed or torque output.
Traditional engine oils have a relatively low viscosity index. That is, the oil viscosity changes significantly with changes in oil temperature. As such, many engine control strategies include temperature modifiers in order to compensate for changes in engine oil viscosity. For example, at lower temperatures (higher viscosity) an increased throttle opening or engine airflow is required to achieve a given engine idle speed or engine torque output compared to running the same engine at a higher temperature (lower viscosity).
Newly developed engine oils may have a higher viscosity index than traditional engine oils, and may display a narrower range of viscosity over a given temperature range. As such, different temperature modifiers may be used than those used for low viscosity index oils. If an engine is refilled with oil having a different viscosity index than expected, the engine control strategies may operate sub-optimally, particularly at low or high oil temperatures. For example, engine control strategies using temperature modifiers for a high-viscosity index oil may command a narrow range of idle throttle openings at low temperature (e.g. cold start conditions). If the engine were refilled with a low-viscosity index oil, the idle speed could be lower than desired, resulting in a stalled engine.
The inventors herein have recognized the above issues and have devised systems and methods to address these issues at least in part. In one example, a method, comprising: setting an engine intake airflow parameter based on an engine oil viscosity index. In this way, engine operating conditions that depend on engine friction and engine intake airflow, such as engine idling speed and engine friction torque, may be determined and implemented with an increased accuracy. This in turn may decrease the possibility of engine stalls and improve engine performance, particularly at low temperatures.
In another example, an engine system comprising: at least one cylinder; at least one piston positioned in the at least one cylinder; an air intake passage coupled to the at least one cylinder; and a controller including instructions to: determine a viscosity of an engine oil in the engine oil system based on a viscosity index of the engine oil and a temperature of the engine oil; and adjust airflow through the air intake passage based on the viscosity of the engine oil. In this way, engine friction may be precisely accounted for based on engine oil viscosity. An engine oil injection system may be coupled to the at least one cylinder. This, in turn, allows for engine intake airflow to be accurately set based on engine speed and load conditions, providing a robust and consistent system that may be adjusted in accordance with changes in engine oil viscosity as the engine temperature increases throughout operation.
In another example, a method for an engine, comprising: during a first condition: increasing engine intake airflow responsive to a first engine oil viscosity and a desired engine idling speed; and during a second condition: decreasing engine intake airflow responsive to a second engine oil viscosity and a desired engine idling speed, the second engine oil viscosity lower than the first engine oil viscosity. In this way engine idle speed can be controlled precisely based on engine oil viscosity, even under conditions where the engine oil viscosity is not immediately known.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.